Abstract We have developed an electric rear-drive unit to enable all-wheel drive (AWD) applications to the compact FF hybrid passenger vehicles. The development is intended to provide a compact and low cost unit with low fuel consumption. The unit newly introduces a two-axis gear train that enables a compact design, an induction motor and an ATF (automatic transmission fluid) stirring resistance restraining structure that contribute to lower fuel consumption. This paper presents the features and performance of the electric rear-drive unit. Introduction In recent years, an increase in the awareness of environmental improvements, such as the reduction of CO2 and generation of cleaner emissions, has promoted the wide use of hybrid vehicles. In the meantime, few compact hybrid passenger vehicles are equipped with AWD, which constitutes an obstacle to the spread of hybrid vehicles to the areas where AWD is necessary in their living environment. Accordingly, three companies under Aisin Group (Aisin Seiki Co., Ltd., Aisin AW Co., Ltd., and Aisin AI Co., Ltd.) have developed, in collaboration with Toyota Motor Corporation, a compact and highly efficient electric rear-drive unit that can be installed in the compact FF hybrid passenger vehicles with minimal changes to the existing packaging. This paper introduces the features of the developed electric rear-drive unit including the structure such as a gear train with a two-axis structure that enables a compact design, the induction motor and the ATF stirring resistance restraining structure that contribute to lower fuel consumption. Objectives of the Development The electric rear-drive unit is developed to incorporate AWD into compact FF hybrid passenger vehicles with the objectives of attaining compact design, lower fuel consumption, and lower costs.i. Compact Design The packaging of the FF vehicle requires minimal changes to accommodate the rear drive unit. The benefit of not requiring a transfer unit and propeller shafts can be capitalized on in the package designing. In order to share the common fuel tank and rear floor with the FF vehicle, the unit was made smaller by adopting a two-axis gear train, in which the motor shaft and differential shaft are placed on the same axis, and high reduction ratio gears. ii. Lower Fuel Consumption In order to realize overwhelmingly low fuel consumption as an AWD vehicle, an induction motor without a permanent magnet is adopted, since the induction motor can minimize loss during the 2WD operation (when the motor is not running). In addition, the stirring resistance restraining structure is adopted to optimize the oil level of the unit by using the scooping-up action of ATF by the gears to supply it in the catch tanks. iii. Lower Costs In order to make an affordable unit for compact vehicles, the number of parts and mechanical processing costs are reduced by integrating the motor and gear compartments and applying shrink fitting to fasten the rotor core and the rotor shaft. Summary of the AWD System The AWD system, which requires no transfers and propeller shafts, is structured by adding an inverter, power cables, and an electric rear-drive unit consisting of a motor, a reducer, and a differential to the base structure of the FF hybrid vehicle. The power control unit directs the motor to add torque to rear wheels when AWD is necessary, for example, during start-up or when the front wheels are in slippery conditions, providing a highly responsive and highly efficient AWD system. Figure 1 describes the structure of the AWD system.Development of Compact Electric Rear-Drive Unit 2016-01-1104 Published 04/05/2016 Yasuaki Tahara, Kazumi Ogawa, Noriaki Nonaka, and Tsuyoshi Kimura Aisin Seiki Co., Ltd. Yukinori Nakamori Aisin AW Co., Ltd. Souichirou Hattori Aisin AI Co., Ltd. CITATION: Tahara, Y ., Ogawa, K., Nonaka, N., Kimura, T. et al., "Development of Compact Electric Rear-Drive Unit," SAE Technical Paper 2016-01-1104,